1. Field of the Invention
The present invention relates to a method of producing a contact lens, which has an identifying mark or indicia such as characters, figures or symbols, or which is partially colored or dyed.
2. Discussion of the Prior Art
Conventionally, hard contact lenses (including gas-permeable hard contact lenses), hydrophilic soft contact lenses or the like have been fabricated by cutting a lens block or blank formed of a suitable lens material into the configuration of a lens, and then finishing the lens by polishing so that the lens obtained has dimensions which meet with a predetermined standard. According to a generally known method, the lens block is initially machined and polished to form a back surface of the lens, to which a special purpose jig is then bonded. With the jig fixed to a lathe, the lens block is further machined and polished to form a front surface of the lens. Thereafter, the lens thus worked is detached from the jig, to thereby give an ophthalmic contact lens.
Some contact lenses produced in the manner as described above have identifying marks or indicia formed in preselected portions of their lens surfaces. The marks include characters, figures, symbols or others, which may permit or facilitate a differentiation between front and back surfaces of the lens or between lenses for left and right eyes, or which may specify the optical qualities of the lens. As specific methods for marking a contact lens, it has been known to use a laser to engrave marks in the lens surface, as disclosed in U.S. Pat. No. 4,194,814, or to deposit on the lens surface a stamp which is impregnated with a printing liquid containing a pigment or dye, as disclosed in JP-B2-1-60804. It has also been known to dye or color a preselected portion of the lens by immersing the lens in a dyeing solution prepared from a water soluble dye and a solvent, with the lens portions other than the preselected portion being covered with a jig, and then drying the lens, as disclosed in JP-A-62-73228.
The marked contact lens produced in the manner as described above tends to suffer from contaminants or dirt attached to its marked region, since the marked region forms a minute recess or protrusion on its lens surface. In the above-described laser-marking technique, for example, the contaminants are likely to enter the marks or craters formed in the lens surface. Further, the formation of the craters results in an undesirably reduced strength of the contact lens which normally has a considerably small thickness. In the marking technique using the pigment or dye, on the other hand, an organic solvent which is usually used for preparing a solution of pigment or dye causes swelling of the marked region of the lens surface to which the solution is applied, whereby the lens surface is made uneven or rough. In this case, contaminants tend to accumulate at the corners formed by the flat portions and protruding or recessed portions of the lens surface. Thus, the conventional marked contact lens is likely to suffer from contaminants accumulated on its marked region, possibly causing irritation of the eye of a lens wearer, for example.